Let´s go:

**[1]** From the DIS (Deep Inelastic Scattering) of eletron-proton, we can imagine that the photon exchanged in te process "sees" a **parton** (possible constituent of the proton) **distribuition**.

We can imagine a cross-section of photons and that constituents of the proton. And we can analyze two situations:

From a cross-section of longitudinal (scalar) helicity photons, $\sigma_{s}$ and a cross-section of transverse helicity photons, $\sigma_{t}$  we can stabilish a relation:

$$ \frac{\sigma_{s}}{\sigma_{t}}  $$ 

And experimentally, we know its values. From the theory, this rate goes to _infinite_ if we are talking about a _spinless constituent_, and goes to _zero_ (at high frequencies of the scattered photon) for a _spin-half constituent_. 
This is how we know that **quarks are spin-half**. (_this answers 4_)

**[2]** There is a excited state of the proton, called $\Lambda^{++}$. This particle is composed by 3 up quarks. As we know the principle of exclusion, we couldn't have 3 fermions _in the same state_ unless there is a additional _degree of freedom_ we are not taking into account.

This additional degree of freedom is the Colour charge. But the fact that we need 3 colours (3 kinds of charge) cames from the choice of the gauge group that describes the strong interactions, the **SU(3)**.

And by this very choice, we have a **non-abelian gauge symmetry** wich means that our _gauge bosons_ (in this case gluons) interact with each other, because in the non-abelian case:

 $$ F_{\mu \nu} = {\partial}_{\mu} A_{\nu} - {\partial}_{\nu} A_{\mu} - iq[A_{\mu},A_{\nu}]    $$

The last term (the _commutator_) of $A_{\mu}$ and $A_{\nu}$ does not vanish and so the Lorentz invariant term in the Lagrangian $ F_{\mu \nu}F^{\mu \nu} $ gives 3-field and 4-field interactions of the gauge bosons. (_this answers 3 and 2_)